An individual's mental state may manifest itself in many different ways. Some of these manifestations are externally detectable, such as facial expressions, heart rate, sweating, and changes to respiration and blood pressure. A person's mental state may be impacted by many types of external stimuli. One increasingly common external stimulus is interaction with a computer. People spend ever-larger amounts of time interacting with computers, and consume a vast amount of computer-delivered media. This interaction may be for many different reasons, such as a desire for educational content, entertainment, social media interaction, document creation, and gaming, to name a few.
In some cases the human-computer interaction can take the form of a person performing a task using the computer and a software tool running on the computer. Examples of this can include creating a document, editing a video, or doing one or more of the other activities enabled by modern computers. The person might find certain activities interesting or even exciting to perform, and might be surprised at how easy it is to accomplish the activities. The person can become excited, happy, or content as they perform those activities. On the other hand, the person might find some activities difficult to perform, and might become frustrated or even angry with the computer, even though the computer is oblivious to his or her emotions. In other cases of human-computer interaction, the person might be consuming content or media, such as news, pictures, music or video. A person's mental state can prove useful in determining whether the person enjoys the media.
In some cases, users can be surveyed to try to determine their mental state in reaction to a stimulus, such as the previously mentioned human-computer interaction. Survey results are often unreliable because the surveys are often done well after the activity was performed. Additionally survey participation rates may be low, and people might not provide accurate and honest answers to the survey. In another manner of determining mental state reactions, people can self-rate media to communicate personal preferences by entering a specific number of stars corresponding to a level of like or dislike. These types of subjective evaluations are, in many cases, neither a reliable nor practical way to evaluate personal response to media. Recommendations based on such methods are imprecise, subjective, unreliable, and are often further subject to problems related to the small number of individuals willing to participate in such evaluations.